Methods for determining a point at which a user is looking are known in the art. The technology is often referred to as eye tracking or gaze detection technology. Eye tracking systems are typically found in two major forms. In one form, a sensor or other eye tracking device is located remote from a user's eye such as in or on a computer, display or similar device.
One known method of eye tracking includes the use of infrared light and an image sensor. The infrared light is directed towards the pupil of a user and the reflection of the light is captured by an image sensor. Through analysis of the reflection point, the direction of the user's gaze may be calculated. One such system is described in U.S. Pat. No. 7,572,008 assigned to Tobii Technology AB, Sweden (the “'008 Patent”). The entire disclosure of the '008 Patent is hereby incorporated by reference, for all purposes, as if fully set forth herein.
Portable or wearable eye tracking devices have also been previously described and are available for commercial purchase. One such eye tracking system is described in U.S. Patent Application Publication Number 2011/0279666 assigned to Tobii Technology AB, Sweden (the “'666 Application”). The entire disclosure of the '666 Application is hereby incorporated by reference, for all purposes, as if fully set forth herein. The '666 Application describes a wearable eye tracking device that requires an external infrared light source to be placed in a scene as a reference point, to assist in determining the direction of a user's gaze.
Existing portable eye tracking systems may suffer severe performance degradation when the equipment moves relative to the wearer's head. For example, glasses may slip relative to a wearer's nose; in addition, a wearer may manually adjust glasses as they are worn. For designs requiring calibration, such movement of the glasses relative to the wearer's head may negate the calibration and significantly degrade the accuracy of the readings. As another example, a single-camera portable eye tracking system may render substantially degraded reading in certain conditions including when the wearer is in the presence of strong light sources; is exposed to direct sunlight; or when the single camera's view is obstructed such as by an eyelash. Furthermore, such single-camera systems may be unable to detect gaze directions at the extremities of a user's field of view.